Why Counting Rapes Is So Tough

My print column this week examines the wide range in estimates for the number of pregnancies that result from rape in the U.S. each year. The cause is the uncertainty both in the number of rapes in the U.S. annually, and in the likelihood that any single rape of a woman could result in pregnancy.

There is no widespread agreement on the number of rapes in the U.S. because of underreporting to police and because some rape counts include offenses that couldn’t result in pregnancy, such as attempted but not completed rape, other sexual assaults, and rape of men. As for the likelihood that a rape could cause pregnancy, calculating that would require reliable figures on rates of ejaculation by rapists, on the exact ages of rape victims, and on the rate of their hormonal-contraceptive use, all of which are known with various degrees of uncertainty.

“The data suck,” said Jonathan Gottschall, a professor of English at Washington & Jefferson College in Washington, Pa. Gottschall co-wrote an article suggesting that, contrary to a suggestion last weekend by Rep. Todd Akin, the Republican U.S. Senate candidate in Missouri, rapes are more likely than other sexual encounters to lead to pregnancy. “The data are not great. There are all kinds of caveats that need to be sprinkled around.”

“It’s a real frustration with the available data,” said Scott Berkowitz, president and founder of the Rape, Abuse & Incest National Network, an anti-sexual violence nonprofit group based in Washington, D.C., about the uncertainty and inconsistency of estimates. RAINN estimates that 3,204 pregnancies result from rape each year in the U.S.

Complicating the issue is that some of the estimates of pregnancies due to rape are based on different years, and the estimates for total number of rapes can fluctuate widely because of small sample sizes and changes in methodology. A Department of Justice victimization survey detected an increase of nearly 50% in rapes and sexual assault in 2010 from the prior year, but the accompanying report cautioned that this was based on just 57 reports of rape in 2010, up from 36 the year before.

“The measurement of rape or sexual assault represents one of the most serious challenges in the field of victimization research,” according to the report.

The Justice victimization survey “doesn’t capture information on whether a pregnancy resulted from rape,” said Shannan Catalano, a statistician with the Bureau of Justice Statistics, the branch of Justice that produces the victimization survey. “The survey does contain a question that asks female victims whether or not they were pregnant at the time of the victimization, but there is a good bit of missing data on this variable due to respondent refusal to answer. There’s also a timing issue because a respondent may not know whether they are pregnant at the time of an interview or for many months afterward.”

Surveys typically produce larger estimates of the number of rapes than do counts of crime reports, but surveys don’t always agree on the extent of underreporting. A survey from the Centers for Disease Control and Prevention put the number of rapes in 2010 at 1.3 million, more than six times the count from the Justice survey.

The Justice survey, the National Crime Victimization Survey, is being revamped to “identify optimal methods for collecting data on rape and sexual assault in self-report surveys,” Catalano said. That involves two projects with outside groups, and nearly $11 million in funds.

“There are numerous reason surveys can undercount rapes, and no survey design is perfect,” Catalano said.

Robert Fleischmann, a theologian and national director of the pro-life Christian group Christian Life Resources in Richfield, Wisc., waded into the numbers debate on Tuesday with a commentary he posted on his group’s website about Akin’s comments. While criticizing the “illegitimate rape” terminology, Fleischmann argued that failure rates for contraceptive techniques that often are above 5% suggest that Akin had a point: Pregnancy rates for rape victims appeared to be lower.

The problem, according to James Trussell, a professor of economics and public affairs at Princeton University whose work was cited by the website Fleischmann quoted for contraceptive failure rates, is that those rates were for a year of use, not for a single instance of sex. The actual rate of pregnancy for couples using contraception from a single instance of sexual intercourse would be much lower.

Asked about this, Fleischmann said that “when people start playing the numbers game, it gets extremely complicated.”

Further reading: A 1996 paper estimated that 32,101 pregnancies result from rape annually in the U.S. A 2000 paper put the number at 25,000. Another 2000 paper tested two surveys conducted identically among college women, with the exception that one asked more detailed screening questions for rape, and found the more detailed survey produced an estimated rate of rapes 11 times larger than the other.

About The Numbers

The Wall Street Journal examines numbers in the news, business and politics. Some numbers are flat-out wrong or biased, while others are valid and help us make informed decisions. We tell the stories behind the stats in occasional updates on this blog.